The present disclosure relates to radiation curable coating compositions that can provide useful coatings and coated surfaces for packaging materials such as metal cans. Currently available radiation curable coatings such as those that cure through ultra-violet (“UV”) radiation or electron beam (“EB”) radiation have a tendency to be inflexible cured coatings that are prone to higher levels of shrinkage. Consequently, coatings utilizing chemistry for such curing have been heretofore recognized by those skilled in the art to be inadequate in terms of direct to metal adhesion, formability, and retort resistance as well as limited in application in terms of adhesion and extensibility within the flexible packaging industry. Attempts to address these concerns can lead to disadvantages of relying on either; (1) processes which require high temperature flash before initiating the radiation cure, as in polyurethane dispersions (“PUD's”), (2) cationic chemistry, which suffers the disadvantage of humidity inhibition of cure, photoinitiator, and currently, high cost due to supply issues, (3) application of high temperature bake, post radiation cure, and/or application of prime coat, to confer adhesion, and/or (4) reliance on conventional solvent and waterborne thermoset chemistries which regress to the disadvantages of releasing volatile organic compounds (“VOCs”), BADGE/NOGE moieties. Thus, any composition which addresses one or more of these issues, while also dispensing with one or more of these disadvantages in radiation cure coatings chemistry would provide one or more benefits for use while positively impacting safety, health, and environmental concerns.
While adhesion promoters are known in the art, it is surprising that higher levels of these compounds than normally used in supplier literature or other published information offer such a significant improvement in adhesion and do not cause severe problems with blush resistance of the cured coating. Higher levels are especially useful on “cleaned only” metal substrates without pretreatment and chrome free substrates.